The Radiation Therapy Oncology Group (R.T.O.G.) is a group of approximately 40 collaborating institutions investigating various protocols in the applications of radiation therapy to the treatment of malignant disease. The protocols involve many disease sites and are increasingly directed toward multidisciplinary approach and intergroup participation. Participation in these studies with careful documentation of the patient's initial disease, accurate dosimetry and the delivery of appropriate therapy, and ongoing follow-up of these patients is essential to the growth of knowledge and the most efficient and successful ways of dealing with cancer.